LVM block size and disk reads for raw devices
Env: AIX 3.2.5, Oracle
Desc: What is the optimal block size to use on reads with Oracle on
raw logical volumes?
Action: This information has been taken from several databases:
The LVM and disk device drivers make requests on 4kb boundaries.
Data can be read from the disk more than 4kb at one time. If
less than 4096 bytes on a read is requested, the disk device
driver will still retrieve 4kb, but will only hand the
application the number of bytes requested.
The controller on the disk reads and writes in increments of
512 bytes. The platter is formatted in 512 byte blocks. When
the disk device driver makes a request for some number of 4kb
blocks, the disk controller does reads in blocks of 512 bytes,
and returns them in increments of 4kb.
Thus, the best block size to use for the reads from Oracle would
be some multiple of 4096.
Support Line: LVM block size and disk reads for raw devices ITEM: X0137L
Dated: August 1995 Category: N/A
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